Which of the two popular browsers is better depends on the platform you are working on. Assuming its Windows:
IE advantages
1. Starts much faster
2. Has a smaller memory footprint
3. Additional tabs do not increase the memory footprint when compared with FF
IE disadvantages
1. Security holes - easily targetted by hackers
2. Relies on the same engine as Windows Explorer so if the browser crashes, your system might go for a spin
FF advantages
1. Faster in rendering CSS layouts
2. Definitely more secure than IE
3. Has lots of cool features and plugins available
FF disadvantages
1. Too much of memory usage. Let you tell you about a little test - have only FF running with 6-8 tabs (depending on your processor speed and RAM) and come back to it in a few hours, you'll see the system performing very slow.
2. takes up a longer time to start (first time)
Have you tried Opera? People just seem to forget this little browser - Or Safari for Windows?